SPATIALVARIATIO NAN DSEASONALIT Y INGROWT HAN DREPRODUCTIO N OF ENHALUSACOROIDES (L.f. )ROYL EPOPULATION S INTH ECOASTA LWATER SOF F CAPEBOLINAO ,N WPHILIPPINE S Spatialvariatio n and seasonality ingrowt h andreproductio n ofEnhalus acoroides (L.f.) Roylepopulation s inth ecoasta lwater s off CapeBolinao ,N WPhilippine s DISSERTATION Submitted in fulfilment of therequirement s of theBoar d of Deanso f Wageningen Agricultural University andth eAcademi c Board of theInternationa l Institute for Infrastructural, Hydraulic and Environmental Engineering for the Degree of DOCTOR tob e defended inpubli c onTuesday , 10Marc h 1998a t 16:00h in Delft by RENÉNADÀ LROLLÓ N bornin Bohol, Philippines Thisdissertatio nha sbee napprove db yth epromoters : DrW . vanVierssen ,professo r inAquati cEcolog y DrW.J . Wolff,professo r inMarin eBiolog y Co-promoter: DrE .D . deRuyte rva nSteveninck ,senio rscientis ta tth edepartmen to fEnvironmenta l Science andWate rResource sManagement ,IH E Authorization tophotocop y itemsfo r internal orpersona l use,o rth e internal orpersona l useo f specificclients ,i sgrante db yA.A .Balkema ,Rotterdam ,provide dtha tth ebas efe eo fUS $1.5 0pe r copy,plu sUS$0.1 0pe rpag ei spai ddirectl yt oCopyrigh tClearanc eCenter ,22 2Rosewoo dDrive , Danvers,M A01923 ,USA .Fo rthos eorganization stha thav ebee ngrante da photocop ylicens eb y CCC,a separat esyste mo fpaymen tha sbee narranged .Th efe ecod efo ruser so fth eTransactiona l ReportingServic eis :9 0541 041 20/9 8US $1.5 0+ US$0.10 . Publishedb y A.A.Balkema,RO.Bo x 1675,3000B RRotterdam ,Netherland s Fax: +31.10.4135947;E-mail : [email protected];Interne tsite :http://www.balkema.n l A.A.BalkemaPublishers ,Ol dPos tRoad , Brookfield,V T05036-9704 , USA Fax: 802.276.3837;E-mail : [email protected] ISBN9 0541 0412 0 © 1998A.A .Balkema ,Rotterda m Printedi nth eNetherland s Mallhusian overfishing occurswhe npoo rfishermen , facedwit h declining catches and lacking any other alternative, initiate wholesale resource destruction in their effort to maintain their incomes. This may involve in order of seriousness, and generally intempora l sequence:(1 ) useo f gearsan dmes hsize s not sanctioned by the government; (2) use of gears not sanctioned within the fisherfolk communities and/or catching gears thatdestro y theresourc e base; and(3 ) useo f "gears" such as dynamite or sodium cyanide that do all of the above and even endanger thefisherfolks themselves . (from Pauly el at. 1989 as qouted in McManus et al. 1992) Alang sa akong inahâng pulô (nga nagsubô tungód sa Mallhusian overfishing): Sa daghang mgâ katuigan nga akó walâ sa imong baybayon, ubân kanunay kanimo ang akong pangisip ug kasingkasing. Kun, dinhà sa imong hunasan, mabanhaw lamang untà, ang napukan nga nagkadaiyang matang nga kinabuhi, nga mata'g usa, sakop sa dili maîukib nga laing kalibutan, walâ na'y dapit, mabisan-asa pa man, nga molabâw sa imong kaanyag ug kaadunahan! Preface This PhD research was financed by the Environmental Ecotechnology programme, an international cooperation between TheNetherlands , ThePhilippine s andUganda , aiminga t executing an integrated environmental research in aquatic ecosystems. Prof. Dr. Wim van Vierssen initiated this international cooperation andmad ei ta reality .A t alate rstage ,Dr .Eri k deRuyte r vanSteveninc k assumed thetas k ofcoordinatin g towards thesuccessfu l execution of various components. In particular, this PhD research benefited from the facilities of a number of institutions, namely the Marine Science Institute (CS, UPDiliman , Philippines), the IHE (Delft, The Netherlands) andth e NIOO-CL (Nieuwersluis, The Netherlands). This PhDresearc h alsobenefite d from thecooperatio n withPau lRiver a whoals oconducte da Ph D research at the same period and study area within the context of Environmental Ecotechnology programme. Operationalizing thegenera l framework ofthi sresearc h hadbeen , invariou s points, difficult. Many thanks to Prof. Wim van Vierssen, Dr. Erik de Ruyter van Steveninck and Dr.Ja n Vermaat whose combined critical ideas were, in allcases , enlightening. I would like toexpres s mygratitud e toth eMarin e Science Institute of the University ofth e Philippines, in general, andt oDr .Migue l D.Fortes , in particular, firstly, for giving me the 'breaks' while being a member of his research team (1988-1992), and,secondly , forkindl y makingavailabl eever y facility Ineede d duringth edat acollectio n (1993-1996).T oal l friends and colleagues at the Institute whotogethe r provided mea scientific home, ... many thanks. The list of your names isjus t too long for a preface page. However, the "seagrass people" cannot be left unmentioned. To Helen D. and Jean B., thank you for the administrative assistance. Thecollectio n offiel d data would nothav e been possible without themagnificien t assistance of Jack Rengel. Aside from being a supportive diving buddy, healway s masterfully piloted the boat to and from the study sites, through the tricky maze inside the reef flat. My acknowledgement also goest oDillar d Knight for doing hisMS c research within thecontex t of this dissertation. The writing of this dissertation was mostly done at the Netherlands Institute of Ecology - Center for Limnology (NIOO-CL). My gratitude goes to all the staffmembers who,i non e way oranother , made mywritin g possible.Th e place itself is wonderful. Maraming salamat! To Analiza andElise , youar ea marvelous team! In you,I always found the ultimate spirit to goo n at various frustrating moments. Finally,I' d like tothan k myparent s Enrique and Esperanza. Inyo usâbkin î nga kalampusan. Ang unang lakang sa akong halayóng panaw nagsugod dinhà kaninyo. René N.Rolló n September 1997 Chapter 1 General introduction Seagrasses are the only submerged flowering plants in the marine environment. They all belong to one order (Helobiae) under the monocotyledon group (i.e.,n o marine dicotyledon exists) and the total number of species so far recorded is less than 60 (57, Kuo &McCom b 1989;49 ,De n Hartog 1970),a negligibl e number(De n Hartog 1970)compare d toth enumbe r of flowering species found inth eterrestria l environment. However, when present, seagrasses and the extensive meadows they can form play an important role in the marine environment. This can be summarized in six basic axioms (Larkum et al. 1989): (1) stability of structure, (2) provision of food and shelter for many organisms, (3) high productivity, (4) recycling of nutrients, (5) stabilizing effects on shorelines and (6) provision of a nursery ground for various fauna including those which are of commercial importance. As primary requirements to photosynthetic organisms, light and mineral nutrition affect seagrasses. Thus, environmental changes, e.g. erosion-derived siltation (EMB Report 1990; Yap 1992; Vermaat et al. in press), which leads to light climate deterioration could spell seriousthrea t toseagras s meadows.I nfact , human activities leading toth ereductio n of water clarity (which includesnutrien t loading,eutrophication , waterquality ,pollution ,an dturbidity ) ranked top on the worldwide list of causes of seagrass declines and disappearances (Short& Wyllie-Echeverria 1996). Because seagrasses need nutrition, an increase in nutrients in the environment,pe rse ,ma yenhanc eseagras sproductivity .However ,excessiv enutrien tincrease s also lead to periphyton and phytoplankton dominance which in effect deprives seagrasses of light. As a net effect, loss of seagrasses is likely to happen (e.g. Cambridge et al. 1986). Aside from environmental changes due to anthropogenic circumstances, seagrasses alsohav e torespon d tonatura l phenomena, e.g. 'wasting'disease ,(Rasmusse n 1977;De n Hartog 1987; Roblee et al. 1991),cyclones , (Cambridge 1975;Poine r et al. 1989) and physical clearances by,fo r instance,dugong s (DeIong h 1995;Pree n 1995).Particularl y for thehighl y diverseS E 'Asia n seagrass meadows,ou r understanding of seagrass responses toenvironmenta l changes, whether natural- or man-induced, is poor. Inth etropica l Indo-West Pacific Region,Enhalus acoroides (L.f.)Royl ei sth elarges t species (Den Hartog 1970;Mene z et al. 1983;Ku o &McCom b 1989;Forte s 1988) among the total of ca. 20 species occurring, and it structurally dominates many seagrass meadows in the region (Erftemeijer 1993;Tomask o et al. 1993;Forte s 1994;Japa r 1994; Kiswara 1994;Lo o et al. 1994; Poovachiranon et al. 1994; Vermaat et al. 1995), often together with Thalassia hemprichii (Ehrenb.)Aschers .(Erftemeije r etal . 1993;Vermaa te t al. 1995;pes .obs. ;se eals o theappendi x summarizing thetaxonom y anddistributio n ofthes etw omos tcommo nspecies) . Thus, it might be argued that understanding the biology of, especially, Enhalus acoroides, could contribute substantially to understanding the effects of environmental changes on seagrass meadows. It is for the above argument that this dissertation focuses on Enhalusacoroides. The main objective of this dissertation is to gain insight into the general question of "how this species 2 . Chapter 1 would respond to environmental changes such as increased turbidity, nutrient loading and siltation". To approach this broad research question, there is a need to gather information on (1) the growth characteristics of Enhalus in the established phase in relation toth e prevailing environmental conditions, (2) the influence of these characteristics on its capacity to vegetatively and sexually reproduce, and (3) the fitness of the propagules (produced by reproduction) inrespons et osuc henvironmenta l changes. Thesethre ebasi cresearc h subtopics form the framework of this dissertation. In the period June 1993-April 1996,a researc h program based on these lines was carried out in Bolinao, NW Philippines. The coral reef system in the area is largely comprised of aree f flat where seagrasses abound (McManus et al. 1992), often in mixed-species meadows (Vermaat et al. 1995) but also in monospecific stands of Enhalus acoroides (pers.